Previous work has shown that biologically functional, non-covalently linked complexes of cytochrome c are generated from several combinations of both overlapping and non-overlapping fragments. We are currently using fast kinetic techniques to study the dynamic events leading to the formation of an ordered, native-like structure. Using fluorescence changes to monitor the reaction, second order kinetics are observed. The rate constants obtained are independent of the nature of the apofragment, but are strongly dependent on the nature of the heme-containing fragment. Thus the reaction rate is identical for combination of (1-38)H with apofragments. (1-104), (23-104), and (56-104), and for combination of (1-25)H with either (1-104) or (23-(104). However the rate constant obtained for complexes utilizing (1-25)H is about fifteen times larger than that observed for complexes of (1-38)H. If the reactions are carried out in the presence of imidazole, the rate constant for (1-25)H complexes increases by a factor of two while the rate constant for (1-38)H complexes increases by over an order of magnitude. These results are interpreted to suggest that the degree of interaction of the heme moiety with the residues of the same chain is an important factor influencing the rate constant.